The invention relates to a turbine for an exhaust gas turbocharger with a turbine casing including a turbine wheel and a vehicle exhaust gas supply passage conducting the exhaust gas to the turbine wheel via a feed passage.
From the series production of combustion engines it is known to employ exhaust gas turbochargers for charging the combustion engines. The exhaust gas turbochargers each comprise a turbine and a compressor. The turbine may be driven by the exhaust gas of the combustion engine. The compressor may be driven via the turbine in order to compress air to be supplied to the combustion engine. This allows the utilization of energy contained in the exhaust gas of the combustion engine so that fuel consumption and CO2 emission may be kept low.
For achieving particularly low fuel consumption values and thus low CO2 emissions the combustion engines are designed in accordance with the so-called down-sizing principle, that is, their sizes are minimized. Here, the combustion engines have a very small engine displacement but because of the compressed air they may provide relatively high specific torque and output power values. Due to the high specific power output the requirements to be met by the exhaust gas turbochargers and in particular by their turbines are increasing. A challenge which must not be underestimated is the realization of a satisfactory instationary behavior of the turbines so that the combustion engines exhibit a good driving behavior.
For Otto engines as well as for Diesel engines, turbines with variable turbine geometries are employed in order to be able to adapt the turbines to various operating points of the combustion engine. Compared to a Diesel engine a variable turbine of an Otto engine must, however, have a particularly wide flow rate range. In particular for achieving an acceptable instationary behavior, e. g. during vehicle acceleration, it is advantageous, in particular in the turbine operating range of low flow rate parameters, i. e. at relatively small flow cross-sections of the turbine, to achieve turbine efficiencies as high as possible.
EP 1 301 689 B1 discloses a turbine of an exhaust gas turbocharger with a turbine casing. The turbine casing comprises a receiving chamber for accommodating a turbine wheel as well as a volute through which the exhaust gas may flow. The turbine further comprises a guide vane mechanism which may be moved in the axial direction, by means of which the exhaust gas flowing from the volute to the turbine wheel may appropriately be directed. This turbine exhibits an inefficient operation.
It is the principal object of the present invention to provide a turbine for an exhaust gas turbocharger which provides for a particularly efficient operation.